v8.0 module release (#22975)

https://mattermost.atlassian.net/browse/MM-52079

```release-note
We upgrade the module version to 8.0. The new module path is github.com/mattermost-server/server/v8.
```


Co-authored-by: Doug Lauder <wiggin77@warpmail.net>

server/channels/app/plugin_test.go

@@ -20,12 +20,12 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
-	"github.com/mattermost/mattermost-server/v6/model"
-	"github.com/mattermost/mattermost-server/v6/plugin"
-	"github.com/mattermost/mattermost-server/v6/server/channels/app/request"
-	"github.com/mattermost/mattermost-server/v6/server/channels/testlib"
-	"github.com/mattermost/mattermost-server/v6/server/channels/utils/fileutils"
-	"github.com/mattermost/mattermost-server/v6/server/platform/shared/mlog"
+	"github.com/mattermost/mattermost-server/server/v8/channels/app/request"
+	"github.com/mattermost/mattermost-server/server/v8/channels/testlib"
+	"github.com/mattermost/mattermost-server/server/v8/channels/utils/fileutils"
+	"github.com/mattermost/mattermost-server/server/v8/model"
+	"github.com/mattermost/mattermost-server/server/v8/platform/shared/mlog"
+	"github.com/mattermost/mattermost-server/server/v8/plugin"
 )
 
 func getHashedKey(key string) string {
@@ -729,8 +729,8 @@ func TestPluginPanicLogs(t *testing.T) {
 		package main
 
 		import (
-			"github.com/mattermost/mattermost-server/v6/plugin"
-			"github.com/mattermost/mattermost-server/v6/model"
+			"github.com/mattermost/mattermost-server/server/v8/plugin"
+			"github.com/mattermost/mattermost-server/server/v8/model"
 		)
 
 		type MyPlugin struct {
@@ -778,7 +778,7 @@ func TestPluginStatusActivateError(t *testing.T) {
 		import (
 			"errors"
 
-			"github.com/mattermost/mattermost-server/v6/plugin"
+			"github.com/mattermost/mattermost-server/server/v8/plugin"
 		)
 
 		type MyPlugin struct {